56 CONTROLLED NATURAL SELECTION 



two specific environments. Species generally 

 occupy common environments without com- 

 petition because there is no crowding there. 

 Common environments do not give rise to 

 specific structures. 



3. New species are formed by differentiation 

 of their specific environments. 



4. The environment becomes similarly sexu- 

 ally and socially differentiated. 



5. Change in environment will produce 

 either evolution or degeneration. If ontogeny 

 and phylogeny give the history of a species, 

 they should also give the history of its en- 

 vironment. 



The earliest forms of life were probably all aquatic. 

 The embryos of nearly all vertebrates and invertebrates 

 have some characters and structures which indicate that 

 their distant ancestors lived in water. 



The conceptions or confessions of faith 

 embodied in most of the above arguments are 

 of course not new ; they have been recalled 

 because they lead the way to the subject 

 under consideration, namely, the power of 

 enemies as selecting agents. 



Particular attention is directed to con- 

 clusions Nos. 2 and 3, which state that 

 common environments do not give rise to 

 specific structures, or in other words, the 



